If you've ever wondered why all the logos on StockLogos are displayed as they might appear on a variety of real-world objects, as shown at right, it's because this is a standard practice in the design world. It's much easier for clients to picture how their new identity will look on the objects for which they're destined, than to simply gaze at artwork and try to imagine how it will be implemented. Creating such mockups has typically required a lot of work, even in the digital era. To meet this need there are sites like Pixeden, which provides a range of free and commercial mockup templates in Photoshop format. This set of 100 free templates on PSDCovers is also worth checking out, and of course searching on "mockup template" will point you to many similar resources. Some are useful, some not so much. So simply having access to a broad, high-quality collection of these might make a lot of sense.
The aptly-named Blank Slate, a new book from German publisher gestalten, comes with a DVD containing more than 400 product dummies of everything from shopping bags and bottles to brochures, each with both black and white backgrounds. The idea is that you flip through the book to find the desired template, then load it into Photoshop. You then incorporate a PDF of your design into the template by using the Transform tool and finally blend the layers to create a convincing look. The book can be purchased on the gestalten site for $60.